EP 0 783 700 B1 relates to a rotor arrangement for an electric machine. A rotor for an electric machine is disclosed, which rotor comprises a coil core, having a center point, wherein a rotational axis runs through the center point. The rotor comprises radially outwardly protruding first and second walls as well as a wire which is wound around a coil core, between the first and second walls, which wire constitutes the winding. Said wire comprises at least one tab which protrudes radially from the center point, pointing from the first wall of the coil core, wherein each tab is formed bent down onto the field winding in the assembled rotor. A notch is formed in the radially outer end of each tab.
U.S. Pat. No. 5,229,672 presents an electric machine which is embodied as a generator and which has a rotor. The electric machine is embodied as a claw pole generator, wherein the claw poles of two claw pole boards engage one in the other. For balancing, notches or drillholes, with which the generator is balanced after completion, are provided arranged distributed with respect to one another along the circumferential direction of the rotor.
FR 2 789 240 A1 relates to a generator for applications in motor vehicles. This generator is also a claw pole generator in which individual claw poles which are formed on claw pole boards engage one on the other. A balancing drillhole is arranged in the region of the claw pole roots which constitute a junction between a plate part of the claw pole board and the individual claw poles which are oriented bent through 90° with respect to said claw pole board.
During the fine balancing of components of an electric machine, for example a generator for use in motor vehicle applications, the rotor must be balanced. This is preferably carried out on the cold-shaped claw poles in the region of the claw pole roots on the back radius by providing fine balance drillholes. The fine balance drillholes constitute a locally concentrated removal of material, as a result of which the rotor of the generator, in particular of a claw pole generator, can be balanced after the mounting. Fine balancing of the rotor of this embodiment of electric machines is thus significant since the rotor in claw pole generators rotates with rotational speeds of the order or magnitude of 18 000 min−1 and higher. The greater the precision with which the balance drillholes, i.e. the fine balance drillholes, can be provided, the greater the quietness of the running of the electric machine which can be achieved. Furthermore, a very long service life of the roller bearings with which the rotor is mounted in the housing, i.e. the stator part of the claw pole generator, can be achieved by extremely precise balancing of the rotor of the claw pole generator.
The provision of fine balance drillholes in the region of the claw pole root on the back radius often leads to misalignment of the drill since drilling occurs at the apex point of the radius of the claw pole root in order to generate removal of material precisely at this point. This can lead to damage to the fan which has already been mounted on the shaft of the rotor or to breaking of the drills.